Expression of PD-1/PD-L1 in children's classical Hodgkin lymphomas.

Background: Although a prognosis of recurrent or refractory childhood Hodgkin lymphoma (HL) is associated with poor outcomes despite intensive therapy, the immune checkpoint inhibitors PD-1/PD-L1 appear to be therapeutic alternatives for advanced adult cases. However, these pharmacotherapies are yet to be studied in a pediatric population.

Procedure: The present study measured the expression of PD-1/PD-L1 in diagnostic samples of children with classical HL, according to the disease course. This study included two groups of patients treated at the Department of Pediatric Oncology, Bordeaux University Hospital-a group of cured or in-remission cases and a group of relapsed or refractory cases. Immunohistochemical analyses of anti-PD-1 and anti-PD-L1 (clone 28-8, companion test for nivolumab) were performed on baseline and follow-up biopsies.

Results: Of the 42 included patients, 31 were cured or in remission and 11 were categorized as relapsed or refractory. At the time of diagnosis, PD-1 expression was low (1-3% of intratumoral lymphocytes labeled) in <20% of cases, whereas PD-L1 was expressed by tumor cells in all cases, and strongly (≥50%) in most cases. There were no significant differences in the expression levels of the two checkpoint molecules between the groups. Initial biopsies showed strong expression of PD-L1, whereas expression of PD-1 was rare.

Conclusions: The identical labeling profiles of the cured and relapsed/refractory patients suggest that comparable responses to inhibitors of the PD1/PDL1 immunological checkpoints could be expected in patients undergoing first-, second-, or third-line therapy.